High Extinction Ratio and Low Temperature Cross-Sensitivity Strain Sensor Based on Vernier Effect Through Hybrid Cascaded Sagnac Loop

Low extinction ratio (ER) and high temperature cross-sensitivity are serious but common problems for most strain sensors based on Vernier effect. In our work, we propose a strain sensor based on Vernier effect. It consists of hybrid cascaded Sagnac loop, one part is a microfiber coupler Sagnac loop (MFC–SL), and the other is a Sagnac loop connected to a Section of polarization-maintaining photonic crystal fiber (PMPCF–SL). Different from the traditional Vernier effect, in the proposed sensor, the spectra of two interferometers shift to opposite directions when the strain changes, which belongs to the enhanced Vernier effect. When ambient temperature varies, the spectra of the two interferometers shift to the same direction, which belongs to the reduced Vernier effect. Thus, its strain sensitivity is improved and its temperature cross sensitivity is reduced. In addition, the MFC–SL and PMPCF–SL exhibit a high fringe ER due to their good transmission of two orthogonal modes. Experimental show that the sensitivity of strain is $- 124.17\,\,\text {pm}/\mu \varepsilon $ , while the temperature sensitivity is only $6.13~\text {pm}/^{\circ }\text{C}$ , and the ER of envelope is about 9 dB. Its robustness can be enhanced by the method of packaging with silicone adhesive. It will have a potential application in the field of strain sensing.